1. Field of the Invention
This invention relates to a process for the preparation of aromatic or heterocyclic azomethines. In a more particular aspect, this invention relates to a process for the preparation of said azomethines by reaction of an aromatic or heterocyclic aldehyde and an aromatic or heterocyclic nitro compound under carbon monoxide pressure.
2. Description of the Prior Art
Numerous azomethines, also known as Schiff bases, aldehyde imines and aldimines, are known to the art. The preparation of azomethines is known to the art and various processes for their preparation are described in the book of Saul Patai "The Chemistry of the Carbon Nitrogen Double Bond" (Interscience Publishers -- 1970). One well known procedure for preparing azomethines comprises reacting an aldehyde and a primary amine. Other procedures known to the art involve the reaction of an aldehyde with (1) an isocyanate EQU Ar--CH=O + R--N=C=O .fwdarw. Ar--CH=N--R + CO.sub.2
or with (2) a sulfurdiimide EQU Ar--CH=O + R--N=S=N--R .fwdarw. Ar--CH=N--R + R--N=S=O
or with (3) a carbodiimide EQU Ar--CH=O + R--N=C=N--R .fwdarw. Ar--CH=N--R + R--N=C=O.
the aldehyde-amine reaction is generally preferred to the other three reactions in the preparation of azomethines principally due to the high cost of the isocyanate, sulfurdiimide and carbodiimide starting materials, but also due to instability of these compounds which make them more difficult to handle than the amines.